Monitor for hvac system

ABSTRACT

Systems and methods for monitoring the performance of an HVAC unit are disclosed. These systems may include a suite of indwelling sensors that are placed within the HVAC unit. The sensors themselves are battery-powered, have energy-efficient components, and communicate wirelessly with a sensor controller. The sensor controller controls the sensors and bridges between local wireless communication with the sensors and wide-area wireless communication to report sensor data to a monitoring station. Control methods for these sensors include instructing them to take and report data only at defined intervals.

TECHNICAL FIELD

The invention relates to heating, ventilation, and air conditioning (HVAC) systems, and more specifically, to monitors for HVAC systems.

BACKGROUND

Heating, ventilation, and air conditioning (HVAC) systems are fundamental to most modern buildings. These systems heat buildings when the weather is cold, cool them when it is warm, and provide ventilation and at least some degree of air filtering. In practice, there are many different types of HVAC systems, but the most common types of air conditioners and heat pumps use vapor-compression refrigeration cycles. Vapor-compression refrigeration cycles cool by using a circulating refrigerant to absorb and remove heat from the building and release that heat elsewhere.

The basic technology behind HVAC systems has been known for decades, and procedures for maintaining and servicing HVAC systems are well established. For example, HVAC systems have traditionally been serviced about once every four months by a trained technician. In some ways, older HVAC systems were more tolerant of certain faults—an HVAC system based on the now-disused refrigerant R-22, for example, could run while significantly low on refrigerant.

Times have changed. Recently, there has been a shortage of trained HVAC technicians, making it more difficult to keep the traditional maintenance schedule. At the same time, systems using newer refrigerants like R-410A are more sensitive to refrigerant-loss faults and must be properly charged with refrigerant in order to operate. Additionally, recent regulatory changes in the United States have made the owners of HVAC systems responsible for any refrigerant leaks from their systems, and have mandated that the owners take action to repair any leaks. All of this potentially creates the need for more technician service calls.

For some HVAC systems, the only performance metric available to building personnel is the temperature of the building relative to a temperature set point. Systems for monitoring the performance of HVAC systems would be helpful in reducing the burden of maintaining the systems. Unfortunately, very few sophisticated HVAC performance-monitoring systems are available on the market. However, a few such systems have been described in the literature. U.S. Pat. No. 9,638,436 to Emerson Electric Co., for example, discloses a system in which sensors are integrated into various parts of an HVAC system to monitor performance.

In order to provide performance information on an HVAC system, sensors may need to be placed in areas that are difficult to reach, difficult to service, and difficult to provide with power, communication, and other technical necessities. These problems may be worse when an existing HVAC system is retrofit with sensors. The way in which the sensors are designed to communicate, coordinate, and use power may have a large effect on the usability and service lifetime of an HVAC monitoring system.

BRIEF SUMMARY

Aspects of the invention relate to systems and methods for monitoring the performance of HVAC units.

In one aspect of the invention, a system for monitoring the performance of an HVAC unit comprises at least one indwelling sensor placed within the HVAC unit and a sensor controller, also placed within the HVAC unit. The indwelling sensor is battery powered and has a transceiver to communicate wirelessly with the sensor controller. In a typical embodiment, that at least one sensor would comprise a plurality of indwelling sensors arrayed around the HVAC unit to monitor, for example, energy consumption, refrigerant temperatures and pressures, and air temperature for discharge and return air, and pressure drop across the HVAC unit filter and evaporator coil. All of the sensors may communicate with the sensor controller wirelessly. The sensors themselves may comprise a common peripheral board to which various temperature, pressure, current, and other types of probes are attached. The common peripheral board is connected to a battery, has the transceiver, and may be magnetically mounted within the HVAC unit.

Another aspect of the invention relates to methods of controlling a sensor network to monitor an HVAC unit. One such method comprises establishing a communication channel with a sensor and accepting a data point from the sensor. The sensor is then provided with a defined time at which the next data point is to be taken. The sensor does not communicate or take data until the defined time. The next data point may be reported to the sensor controller at a time different from the defined time. The defined time may be unique to each sensor and may include an offset that takes into account the time it takes to instruct the sensors.

Yet another aspect of the invention relates to a method for monitoring refrigerant charge in an HVAC unit. In a method according to this embodiment, each HVAC unit has identifying indicia, such as a QR code. When the unit is charged with refrigerant by a technician, the technician scans or otherwise enters the identifying indicia and then enters the amount of refrigerant added. The data is sent to a monitoring station, which determines whether the refrigerant leak rate is too high and, if so, sends messages indicating that a refrigerant leak is probable.

Other aspects, features, and advantages of the invention are set forth in the description that follows.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a schematic diagram of a system according to one embodiment of the invention, illustrating the placements of sensors in an HVAC unit;

FIG. 2 is a schematic illustration of a peripheral sensor board in the system of FIG. 1;

FIG. 3 is a side elevational view of a peripheral sensor board with a sensor boom;

FIG. 4 is a schematic illustration of a sensor controller in the system of

FIG. 1;

FIG. 5 is a flow diagram of a method for controlling the sensors in the system of FIG. 1;

FIG. 6 is an illustration of a monitoring display using the system of FIG. 1;

FIG. 7 is an illustration of the monitoring station of the system of FIG. 1 and the various elements to which it is connected or with which it communicates; and

FIG. 8 is an illustration of a system for direct monitoring of refrigerant consumption in HVAC units.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of a system, generally indicated at 10, according to one embodiment of the invention. System 10 includes a sensor controller 12 in communication with a suite of indwelling sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 that are positioned at various locations in an HVAC unit 50. The sensor controller 12 is itself in communication with a monitoring station 52, as will be described below in more detail.

In the view of FIG. 1, the HVAC unit 50 is an air conditioning unit. However, the HVAC unit 50 could also be a reversible heat pump system, or any other similar kind of system. The HVAC unit 50 is shown schematically in FIG. 1, as are the positions of the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32. The HVAC unit 50 has a compressor 54, a compressor discharge line 56 that leads to a condenser 58, and a refrigerant liquid line 60 that leads from the condenser 58 to an evaporator 62. Interposed in the liquid line 60 are a drier 64 and a flow metering device 66. The flow metering device 66 may be a thermostatic expansion valve or another similar device. Additionally, the condenser has a fan 68 and the evaporator 62 has a blower 68.

The HVAC unit 50 is thus intended as a typical example of an air conditioning system. Countless variations are possible, and for ease of description, many possible elements and variations are omitted. For example, in a typical HVAC unit, the components may be placed in two separate enclosures or housings, with the compressor 54 and condenser 58 outside and the evaporator 62 inside the building. The details of the HVAC unit 50 itself are not critical.

Generally speaking, the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 in the suite can be divided into three categories: power usage sensors, refrigerant temperature/pressure sensors, and air sensors. Together, the suite of sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 monitors a variety of things within the HVAC unit 50, including the electrical draw of the HVAC unit 50 as a whole; the electrical draw of certain components; the temperature and pressure of the refrigerant at certain points; and the temperature, pressure, and humidity of the air at certain points.

As an example of power usage sensors, sensor 14 monitors the total current draw of the HVAC unit 50 and may be placed on the power cables that feed the system. Sensor 14 would typically include a clamp-on portion or probe that measures current flow through a cable inductively. Similarly, sensor 16 monitors the current draw of the compressor 54, sensor 20 monitors the current draw of the condenser 68, 4and sensor 24 measures the current draw of the evaporator 70.

As an example of refrigerant temperature/pressure sensors, sensor 18 is positioned to monitor the compressor 54 refrigerant discharge pressure and temperature. Typically a temperature probe connected to sensor 18 would be placed in contact with the exterior of the discharge line 56. The temperature probe would typically be a device that establishes an electrical signal in response to temperature, such as a thermocouple or a thermistor. For example, the Littelfuse USP10982 thermistor probe (Littelfuse, Inc., Chicago, Ill., US) is one suitable type of temperature probe. The pressure probe, also in communication with sensor 18, may be coupled with a fitting, such as a connector, that allows it to be inserted into the discharge line 56. For example, the Honeywell PX3 series of pressure sensors (Honeywell International, Inc., Fort Mill, SC, US) may be suitable pressure probes for this application. Installation of these pressure probes would usually involve installing a T-fitting in the line and connecting the pressure probe to the open port in the T. Similarly, sensor 32, in the suction line 68 between the evaporator 62 and the compressor 54, measures refrigerant suction pressure and temperature and has similar components to sensor 18. Sensor 22, in the liquid line 60, measures the refrigerant temperature at that point, and may have the same type of temperature sensor, but no pressure sensor.

In the illustrated embodiment, the air sensors are mostly clustered around the evaporator 62. For example, sensor 26 measures the return air temperature, humidity, and pre-filter static air pressure. Similarly, sensor 30 measures the discharge air temperature, the humidity, and the air pressure and/or pressure drop across the evaporator coil 62. These two sensors 26, 30 generally have the same components. Sensor 28 measures the static air pressure after the system air filter.

While the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 are described separately here for ease of explanation, in some embodiments, several sensors may be consolidated together and may, e.g., share the same electronics. This will be explained below in more detail.

The sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 may be constructed in any number of ways. As those of skill in the art will appreciate, in many cases, it is possible to obtain individual commercial, off-the-shelf temperature, pressure, current, and humidity sensors that are completely self-contained and even include wireless communication capabilities.

However, self-contained, off-the-shelf sensors may have downsides in some cases. The sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 are intended to be placed in locations that may be hard to reach, locations in which a permanent power supply is unavailable. For those reasons, they are typically designed to be battery powered. Moreover, it is highly advantageous if the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, and system 10 in general, are designed to maximize the battery life of the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, because replacing batteries may be difficult.

Thus, although commercial, off-the-shelf sensors with their own integrated electronics may be available, that type of sensor may not be adapted for long-term indwelling use, and may use too much power. For that reason, it may be more advantageous to use custom electronics in order to minimize power usage and prolong battery life.

As was noted briefly above, while the roles of each of the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 may be different from one another, and they may have different types of probes (e.g., current, temperature, pressure, etc.), it is advantageous if the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 are designed such that, as much as possible, each sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, regardless of its specific role, has the same electronics.

FIG. 2 is a schematic illustration of a common peripheral board, generally indicated at 100. The peripheral board 100 includes connecting, signal conditioning, and communications hardware. As shown, it includes a first connector 102, a second connector 104, and a third connector 106. The first connector 102 may be configured to receive input from a current probe 108 to determine power usage, the second connector 104 may be configured to receive input from a pressure probe 110, and the third connector 106 may be configured to receive input from a temperature probe 112. As can be seen in FIG. 2, all three probes 108, 110, 112 connect with the connectors 102, 104, 106 with wired connections. The connectors 102, 104, 106 may be terminal blocks for the insertion of wires, or they may be, e.g., female electrical connectors that accept complementary male connectors that are provided on the wires.

In addition to the connectors 102, 104, 106 for probes 108, 110, 112, the peripheral board 100 also includes a battery connector 114 that connects to an external battery 116. The battery may be, for example, 3.6V, 2.4 Ah lithium battery. As will be explained below in more detail, the use of custom hardware as well as specific communication protocols preferably makes the battery life of such a battery at least 5 years. In some cases, the battery life may extend to 8 years.

The particular electronics on the peripheral board may vary from embodiment to embodiment depending on what is needed to read the various probes 108, 110, 112. The following description assumes that each probe 108, 110, 112 establishes an analog electrical signal in response to the conditions that it is measuring. For example, the various probes 108, 110, 112 may produce analog voltage signals of 0-5V, 0-10V, etc. The following description also assumes that no amplifiers or other signal conditioning electronics are needed to read these analog signals. If amplifiers, filters, or other such devices are needed, they may be provided on the peripheral board 100 before any other electronics.

As shown in FIG. 2, the peripheral board 100 includes an input-output interface 118. In some embodiments, each connector 102, 104, 106 (i.e., each data channel) may have its own input-output (I/O) interface. In some cases, a single input-output device may have multiple channels. For ease of illustration, only a single I/O interface 118 is shown in FIG. 2. While any number of devices may be used to manage input and output in the peripheral board 100, the I/O interface 118 may be, for example, a UART for serial I/O.

From the interface controller 118, signals from the probes 108, 110, 112 are sent to an analog-to-digital (A/D) converter 120. The peripheral board 100 also includes a local controller 122 that coordinates the activities of the peripheral board 100. The local controller 122 may be a microcontroller, a microprocessor, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or any other device capable of performing the functions ascribed to it in this description. The local controller 122 is connected to a transceiver 124 with an antenna 126. The transceiver 124 communicates wirelessly with the sensor controller 12 to send and receive data and for synchronization and control, as will be described below in more detail. The transceiver 124 may, for example, be a BLUETOOTH® low energy (BLE) chipset. Alternatively, the peripheral board 100, and system 10, may use a communication protocol such as that defined in IEEE 802.15.4. Other components, such as memory, are not shown in the view of FIG. 2, although they would be present in a peripheral board 100.

Although the various components are shown in FIG. 2 as being directly connected, in some embodiments, all components may communicate via an internal data bus, and other components, such as memory, will typically be included. Additionally, although the components are shown separately in FIG. 2, they may be combined in some embodiments as a system-on-a-chip or another type of integrated circuit that includes all components. For example, the core functions of the peripheral board, including the local controller 122, the transceiver 124, and the I/O interface 118, could be performed by a BMD-300 series ultra-low power BLUETOOTH® smart module (Rigado, Inc., Salem, Oreg., U.S.).

With the arrangement shown in FIG. 2, the probes 108, 110, 112 would typically have limited onboard electronics and would leave all signal conditioning and communication tasks to the peripheral board 100. The peripheral board 100, with appropriate probes 108, 110, 112 connected, could serve as any of the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32. Additionally, as was noted above, one peripheral board, properly outfitted with several probes 108, 110, 112, could serve as several of the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32.

The peripheral boards 100 would typically be attached within the HVAC unit 50 using permanent magnets 128 on the undersides of the peripheral boards 100. Alternatively, mounting clips or other such structures may be used. To protect them from the surrounding environment, the peripheral boards 100 may be encapsulated in resin or placed within a case.

For sensor 26, which measures air pressure, temperature, and humidity, and for sensor 28, which measures air pressure, the physical arrangement of the board may be somewhat different. FIG. 3 is a side-elevational view of a peripheral board 150 that is suitable for these sensors 26, 28. In both cases, sensors 26 and 28 involve probes that must be placed in the airstream to read properly. For that reason, the peripheral board 150 may include a rigid boom 152 that is connected to the circuit board 154 with a fastener. The probes for air pressure, humidity, and temperature may be located along the boom 152 or in a space 156 at the end of the boom 152. The electronics on the peripheral board 150 may otherwise be similar to the electronics of the peripheral board 100 described above. In other embodiments, air pressure, humidity, and temperature sensors may simply be built into or mounted on the peripheral board 150 in another manner, e.g. by surface mounting.

FIG. 4 is a schematic illustration of the sensor controller 12 of system 10. The sensor controller 12 is also an indwelling component, installed in or near the HVAC unit 50 so as to be in wireless communication with the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32. Preferably, the sensor controller 12 is installed in an area where a permanent power source is available. Typically, this permanent power source will be a 24 VDC power output from the HVAC unit 50. Because the sensor controller 12 will often operate at much lower voltages, a driver 200 receives power from the HVAC unit and outputs a voltage suitable for the sensor controller 12 which, in this embodiment, is assumed to be 5VDC.

The driver 200 would typically be an AC-DC or a DC-DC power converter, and may be of any type. Although shown in FIG. 4 as a separate component, the driver 200 may be integrated into the electronics of the sensor controller 12, such that the sensor controller 12 can simply receive higher voltages and convert them to lower voltages onboard.

As noted briefly above, the sensor controller 12 has several functions in system 10. First, it collects data from the various sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32. The sensor controller 12 may also convert that collected data from a raw form into a more finished form. For example, the calibrations needed to convert probe data from raw data to readable temperatures, pressures, humidity levels, and power consumption levels may be applied by the sensor controller 12. Additionally, the sensor controller 12 reports the collected and converted or conditioned data to the monitoring station 52.

In most cases, the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 will communicate using different frequencies and networking protocols than the network to which the monitoring station 52 is connected, although it is possible that in some cases, the components may all communicate using the same frequencies and networking protocols. Thus, on the hardware level, one distinguishing characteristic of the sensor controller 12 of this embodiment is the ability to bridge between, and to communicate using, two separate communication networks: a local-area network (LAN) used by the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, which will typically use a networking protocol such as BLE; and a wide-area network (WAN) used to cover longer distances between the sensor controller 12 and the monitoring station 52.

The monitoring station 52 will usually be remote from the HVAC unit 50, and may be operated by a party different than the owner and operator of the HVAC unit 50 itself. In order to facilitate remote monitoring by a third party, the WAN with which the WAN transceiver 204 communicates will usually be a cellular data network, such as a 4G LTE cellular data network, that uses cellular technology to connect to the Internet. Using this type of network, the sensor controller 12 can communicate with virtually any system in the world. So-called LoRA long-range wireless communication networks may also be used. The monitoring station 52 itself may be cloud-based, i.e., it may be part of a shared Internet server on which various applications are run to perform the functions ascribed to the monitoring station 52 here.

In the illustration of FIG. 4, the sensor controller 12 has two transceivers, a LAN transceiver 202 and a WAN transceiver 204. As was described above, for purposes of this description, the LAN transceiver 202 can be considered to be a BLE transceiver, and the WAN transceiver 204 can be considered to be a cellular network transceiver.

For simplicity of illustration, the only other component shown in FIG. 4 is a central unit 206. The central unit 206 is responsible for receiving and processing data from the LAN transceiver 202, controlling the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 and directing their data acquisition, as will be described below in more detail, and sending data to the monitoring station 52 through the WAN transceiver 204. The central unit 206 may be a microprocessor, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or any other device capable of performing the functions ascribed to it in this description.

The components 202, 204, 206 may communicate via an internal bus, and other components that are not depicted, like memory, will typically be present. As was described above with respect to the peripheral board 100, the components 202, 204, 206 may also be integrated into a system on a chip or another, similar type of integrated circuit device.

While the components of the sensor controller 12 may be any components capable of performing its functions, in some embodiments, it may be helpful if the peripheral boards 100 and the sensor controller 12 share components to the extent possible. For example, the sensor controller 12 may use the same BMD-300 smart module as the peripheral boards 100. It may also have an additional chipset for cellular communications, for example, a PINNACLE™ cellular chipset (Laird Connectivity, Akron, Ohio, U.S.).

As was noted briefly above, in system 10, it is advantageous if the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 can remain in place without requiring battery replacement for a span of years, typically at least 5 years, and in some cases, at least 8 years. Obviously, that kind of longevity might be achieved simply by using a high-capacity battery, although there are limits to what even a high-capacity battery can achieve. Thus, in system 10, both the hardware and the software are engineered to use as little energy as possible.

Part of the energy efficiency lies in when and how the sensor controller 12 queries the various sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 for data. Here, there are several applicable principles. First, it is advantageous if the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 take their readings at the same time, in order to provide a snapshot of the performance of the HVAC unit 50 at a particular instant in time. However, the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 may report their readings from that particular instant in time at staggered times. Second, while it is advantageous to report the performance of the HVAC unit 50 in real time, “real time” in this application may refer to a data acquisition rate of one data point every few minutes. For example, the data acquisition rate may be one data point from each sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 every 5-10 minutes. In some embodiments, the data acquisition rate may be one data point every 15 minutes or lower. However, there are situations in which a higher data acquisition rate may be advantageous. If a problem has been detected or if a repair is underway, for example, the data acquisition rate may be much faster. As will be described below in more detail, the data acquisition rate is adjustable to suit the situation.

FIG. 5 is a schematic flow diagram of a method, generally indicated at 300, for synchronizing and querying data from the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32. Method 300 exemplifies the tasks performed by the sensor controller 12, begins at task 302 and continues with task 304. Task 304 is a decision task, the start of an initialization loop for all of the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32. If all of the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 have not been initialized and read (task 304: NO), method 300 continues with task 306.

In this description, it is assumed that the peripheral boards 100 for the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 are paired with the sensor controller 12 on installation or, at least, prior to the execution of method 300. The term “paired” may refer to a BLE pairing process per se if BLE is used or, more generally, it may refer to any process by which the sensor controller 12 is made aware of the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 that are to report to it in system 10, such that the sensor controller 12 will not accept input from any sensors save for the ones with which it has been paired. Burned-in hardware addresses, like MAC addresses, may be used in the pairing process.

In task 306, the sensor controller 12 wakes and establishes a connection with one of the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32. This is done according to the standard for the communication protocols that are being used. At the completion of task 306, a wireless communication channel has been established between the sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 and the sensor controller 312. Method 300 continues with task 308.

In task 308, the sensor controller 12 acquires a point of data from the sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, i.e., the peripheral board 100, with which it is communicating. Once a wireless communication channel is established in task 306, communication may use any number of different transport protocols and any number of data formats. The present inventors have found that the User Datagram Protocol (UDP) is a particularly convenient protocol to use for data transport, primarily because of its simplicity. Other data transport protocols, such as MQTT, may also be used. The data from the various probes 108, 110, 112 may be transmitted in a data interchange format, such as JSON. In some cases, a more complex data description language, such as XML, may be used.

Method 300 continues with task 310. Once a data point has been acquired from a particular sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, the sensor controller 12 puts that sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 to sleep, i.e., in a standby mode. Before doing so, the sensor controller 12 provides the sensor with instructions on when to wake and take the next data point. Those instructions may be, e.g., in the form of a single number, transmitted by the sensor controller 12 to the particular sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, that represents the number of seconds or milliseconds until the next data collection time.

In task 310, the instructions on when to wake and take the next data point are unique for each sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32. More specifically, assume that the sensor controller 12 wishes the next data point to be taken x seconds from the present time. (As explained above, the value of x may vary considerably, but for these purposes, may be assumed to be in the range of 300-900 seconds, 5-15 minutes.) Assume also that the sensor controller 12 queries the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 and provides instructions serially, one at a time. It takes some amount of time to do this for each sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32. To compensate for the amount of time it takes to query and instruct the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, and to ensure that the data points are taken as simultaneously as possible, the actual wake time provided to the sensor is x-y, where y is an offset that represents the time consumed in instructing the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32. The offset y may be expressed in milliseconds, seconds, or some other unit, and is usually established by a counter that the sensor controller 12 starts when the first sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 is queried. Generally speaking, the offset y for each successive sensor will be greater than the offset for the last sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32.

At the same time, either the sensor controller 12 or the individual sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 may select a time at which the sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 is to report the data point that has been acquired. As was described briefly above, the time at which the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 take the data point should be as simultaneous as possible. However, they need not report the data simultaneously. Therefore, an additional reporting time is chosen at which the sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 will report the data that has been acquired. That reporting time may be specifically chosen for each sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 within a window of, e.g., a few seconds after the designated data acquisition time.

Once task 310 is complete, the sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 that was queried goes into a standby mode until time x -y. Control of method 300 returns to task 304. If all sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 have been initialized (task 304:YES), control of method 300 passes to task 311; if all sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 have not yet been initialized (task 304:NO), control of method 300 continues with task 306, and the next sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 is selected and initialized.

When control of method 300 is passed to task 311, the accumulated data is sent by the sensor controller 12 over a network for storage and processing by the monitoring station 52, as will be explained below in more detail. Method 300 then continues with task 312. When task 312 initiates, it is assumed that the time set by the sensor controller 12 has elapsed, and it is time to take the next data point.

Tasks 312-316 of method 300 proceed much as tasks 306-310. In task 316, the sensor controller 12 sets a new time x as the new data acquisition interval and passes new offsets y to the various sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 as they are queried and instructed. Generally speaking, the data acquisition interval is preprogrammed, although it may be adjusted manually by a user at the monitoring station 52. Additionally or alternatively, if a problem of some sort is detected (as will be described below in more detail), the data acquisition interval may be shortened for a single cycle or for a number of cycles until the problem is resolved or until the monitoring station 52 instructs the sensor controller 12 to do otherwise.

Once task 316 is complete, control of method 300 passes to task 318, a decision task. In task 318, all sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 have been read in this cycle (task 318:YES), control of method 300 passes to task 319. If all sensors have not yet been read in this cycle (task 318:NO), control of method 300 returns to task 312 and the next sensor 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 is read and instructed.

In task 319, the accumulated data is sent over a network for storage and processing by the monitoring station 52. Method 300 continues with task 320.

In task 320, if there is some reason to terminate (task 320:YES), method 300 terminates at task 322. If there is no reason to terminate (task 320:NO), control of method 300 returns to task 312. Typically, once method 300 is initiated, it will continue indefinitely. However, the monitoring station 52 may send instructions to terminate and re-initialize. This may be done, for example, so that one or more of the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 can be placed or replaced. Task 320 may provide an opportunity for the monitoring station 52 to send additional or different instructions to the sensor controller 12.

Monitoring, Fault Detection, and Diagnosis

FIG. 1 depicts a simple monitoring station 52. In various embodiments and installations of system 10, anything from simple manual monitoring of the HVAC unit 50 to automated fault detection and diagnosis may be implemented. The actual functions of the monitoring station 52 in any particular embodiment will depend on a number of factors, including cost and the desires of the HVAC unit 50 operator. As may be apparent from the description above, the data gathered by the sensors 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 at the direction of the sensor controller 12 represents much of the information that a human technician would gather in diagnosing or predicting a problem with the HVAC unit 50.

Typically, the data from the sensor controller 12 would travel through a WAN, such as a cellular data network, to a cloud-based server that serves as the monitoring station 52. The monitoring station 52 would generate an appropriate interface, e.g., in the form of a website. HVAC unit operators can log on to the website in order to view the status of their unit.

FIG. 6 is an illustration of a summary screen, generally indicated at 400, of a monitoring interface according to one embodiment of the invention. In any interface, some of the data may be presented as gathered, while other data may be used to calculate metrics that are presented in the interface. Moreover, data may be presented in any format, including numerically, as part of graphs that track values over time or relative to some other value, and as part of gauges or other such graphical elements that are used to display a value relative to a normal range.

In the illustration of FIG. 6, the screen 400 includes suction pressure and liquid pressure graphical gauges 402, 404 that display suction pressure and liquid pressure relative to normal and abnormal ranges, as well as suction temperature and liquid temperature graphical gauges 406, 408. This data can be directly gathered by the sensors 32, 22 in the suction and liquid lines 68, 60, respectively. Condenser fan amps, supply fan amps, and compressor amps are all displayed as graphs 410, 412, 414 versus time, all taken from the current sensors 16, 20, 24 in those locations. The system superheat and subcool are displayed in separate graphical elements 416, 418. Superheat and subcool are derived quantities calculated from sensor data in the conventional way.

This particular screen 400 also provides separate graphical elements displaying ambient temperature 420, discharge air temperature 422, return air temperature 424, filter pressure drop 426 and condenser pressure drop 428. The screen 400 also provides an efficiency graph 430, measuring rated efficiency against actual, calculated system efficiency.

Some interfaces may include fault detection capabilities, although a monitoring station 52 or interface need not have fault detection capabilities in all embodiments. As a first step, most fault detection involves comparing the value of a single variable or a range of variables to baseline values. The baseline values may be established for the particular HVAC unit 50 based on actual data, or they may be established based on measured or rated values for a number of HVAC units of the same type.

Table 1 below provides an example of a decision tree for determining when a system fault has occurred, and the type of the fault, based on whether certain values are higher or lower, as compared with their baseline.

TABLE 1 Decision tree for various types of faults based on multiple system values. Indoor Suction Head Compressor Temperature Fault Type Pressure Pressure Superheat Subcooling Amps Differential Low Charge Down Down Up Down Down Down Over Charge Up Up Down Up Up Normal or Down Low Indoor Down Normal or Down Normal or Normal or Up Air Flow Down Up Down Dirty Up Up Down Down Up Down Condenser Coil Mild Down Normal Up Normal or Down Down Restriction Up Severe Down Normal or Up Up Up Down Restriction Up Low Down Down Down Down Down Down Evaporator Air Flow Inefficient Up Down Up Up Down Down Compressor Non- Up Up Down Normal Up Down Condensables

If a fault is detected, the monitoring station 52 may display it in the interface 400. Other steps may also be taken. FIG. 7 is an illustration showing the monitoring station 52 and the components to which it may be connected or with which it may communicate.

As FIG. 7 illustrates, the monitoring station 52 may communicate in a variety of ways. The monitoring station 52 may, for example, communicate via the Internet with an app on a mobile device, and may provide alerts via that app. In some cases, the monitoring station 52 may be connected to, or communicate with, other types of gateways, networks, and services in order to send messages and alerts using those services. As a simple example, the monitoring station may be connected to or communicate with an SMS gateway 502 in order to send SMS text message alerts to building and maintenance personnel. In some cases, the SMS gateway 502 may also accept SMS text message commands and forward them to the monitoring station 52 to control system 10. The monitoring station 52 may also include, communicate with, or be connected to a cellular gateway 504 to place automated notification calls to responsible individuals. If the building in which the HVAC unit 50 is installed has a building information system 506 or another type of automated system, the monitoring station 52 may be connected to that in order to provide alert messages.

The monitoring station 52 also includes or is connected to a database. The monitoring station 52 will typically keep records, both of the status of the HVAC unit 50 and of any faults or problems that are detected. These records will typically be kept for maintenance purposes, although they may also serve certain regulatory purposes.

Monitoring of Refrigerant Fill

As described above, system 10 is capable of detecting refrigerant leaks and low-refrigerant faults. In addition to the monitoring methods described above, it is possible to detect refrigerant leaks by other methods. These methods may be integrated into monitoring systems like system 10 described above, or they may be implemented separately, without the other components and functions of system 10.

FIG. 8 is an illustration of a system, generally indicated at 600, that specifically monitors refrigerant fill and levels. In system 600, each HVAC unit 602 has identifying indicia 604, such as a QR code. When a technician fills the HVAC unit 602 with refrigerant, he or she uses a mobile device 606 to scan the identifying indicia 604 for the HVAC unit 602 and then enter the quantity of refrigerant that is added. That information is checked to eliminate obvious bad input and transmitted to a monitoring station 608. The monitoring station 608 records the data in a database 610, indexed by the particular HVAC unit 602, and compares it with past records for that HVAC unit 602 and with norms for the particular type of HVAC unit 602.

If the monitoring station 608 determines that the HVAC unit 602 is losing too much refrigerant, various steps may be taken to alert the operator of the HVAC unit 602 that maintenance or repair is needed. First, the technician may be alerted via app on the mobile device 606 that there is a probable refrigerant leak that requires maintenance. SMS and cellular gateways 612, 614 may be used as described above to provide immediate notifications as well, and the monitoring station 608 may communicate with the building information system 616 for the building where the HVAC unit 602 is located.

If no action is taken to remedy the possible refrigerant leak detected by the monitoring station 608, the notifications may be repeated. In some cases, to satisfy regulatory requirements, paper letters may be automatically generated by the monitoring station and sent by the operator of the monitoring station 608 to the operator of the HVAC unit 602 when a fault is detected and at intervals thereafter if no repair has been logged. The database 610 also serves to keep regulatory compliance records, such as the date on which a fault was detected and the date or dates on which notifications were sent.

While the invention has been described with respect to certain embodiments, the description is intended to be exemplary, rather than limiting. Modifications and changes may be made within the scope of the invention, which is defined by the appended claims. 

What is claimed is:
 1. A monitoring system, comprising: at least one indwelling sensor adapted to measure one or more characteristics of an HVAC unit, the at least one sensor having a sensor transceiver, and a battery; and a sensor controller having a first transceiver and a second transceiver, the first transceiver being adapted to communicate wirelessly with the sensor transceiver.
 2. The monitoring system of claim 1, wherein the at least one indwelling sensor further comprises: a peripheral board, the peripheral board having the sensor transceiver and being connected to the battery; and one or more probes connected to the peripheral board.
 3. The monitoring system of claim 2, wherein the one or more probes comprise a temperature probe, a liquid pressure probe, an air pressure probe, or an electric current probe.
 4. The monitoring system of claim 2, wherein the peripheral board further comprises at least one permanent magnet adapted to attach the peripheral board within the HVAC unit.
 5. The monitoring system of claim 1, wherein the sensor transceiver and the first transceiver are adapted to create a local area network for the at least one sensor and the second transceiver is adapted to communicate with a wide area network.
 6. The monitoring system of claim 5, wherein the local area network uses BLUETOOTH™ communication protocols and the wide area network is a cellular network.
 7. A method for controlling an indwelling network of sensors in an HVAC unit, comprising: establishing a communication channel with a first sensor; accepting a first data point from the first sensor; and instructing the first sensor to obtain a next data point at a first defined time and to report the next data point at a second defined time, the second defined time being different than the first defined time; and causing or allowing the first sensor to wait without communicating or gathering data until the first defined time.
 8. The method of claim 7, wherein the first defined time includes a first offset representing a sensor instruction time period.
 9. The method of claim 8, further comprising: establishing a communication channel with a second sensor; accepting a second data point from the second sensor; and instructing the second sensor to obtain a second next data point at a third defined time and to report the second next data point at a fourth defined time, the fourth defined time being different than the third defined time, the third defined time including a second offset, different from the first offset, representing the sensor instruction time period.
 10. A method of gathering data from an HVAC unit, comprising: establishing a communication channel with a sensor controller; reporting a first data point to the sensor controller; accepting a unique defined time at which to gather a second data point; waiting without communicating or gathering data until the unique defined time; and gathering the second data point at the unique defined time.
 11. The method of claim 10, further comprising reporting the second data point to the sensor controller at a second time different from the unique defined time.
 12. A method for monitoring an HVAC system, comprising: causing or allowing a sensor controller to gather data at a defined interval from one or more indwelling sensors installed within the HVAC system, the sensor controller further causing or allowing the one or more indwelling sensors to wait without communicating or gathering data during the defined interval, the one or more indwelling sensors communicating with the sensor controller wirelessly via a local area network; receiving the data from the sensor controller over a wide area network different from the local area network; and processing the data to determine a status of the HVAC system.
 13. The method of claim 12, further comprising determining the source of a fault in the HVAC system.
 14. The method of claim 13, wherein said determining comprises comparing multiple metrics within the processed data with baseline values for the multiple metrics.
 15. The method of claim 14, further comprising establishing an interface that allows a user to access the processed data, view at least some of the multiple metrics, view the status of the HVAC system, and receive alerts related to the determined fault.
 16. The method of claim 12, wherein the sensor controller is an indwelling component installed within the HVAC system.
 17. The method of claim 12, wherein the one or more indwelling sensors are battery powered.
 18. The method of claim 12, further comprising determining a new defined interval and communicating the new defined interval to the sensor controller. 